General background information concerning self-coherent detection may be found for example in the following references:    [1] Moshe Nazarathy, Alik Gorshtein, and Dan Sadot “Doubly-Differential Coherent100 G Transmission: Multi-Symbol Decision-Directed Carrier Phase Estimation with Intradyne Frequency Offset Cancellation,” SPPCom, Karlsruhe, Germany (Jun. 21-24, 2010).    [2] E. Ip and J. M. Kahn, “Fiber Impairment Compensation using Coherent Detection and Digital Signal Processing”, J. of Lightwave Technol., vol. 28, no. 4, pp. 502-519, Feb. 15, 2010 (Invited Paper)    [3] S. Zhang, P. Y. Kam, J. Chen, and C. Yu, “Decision-aided maximum likelihood detection in coherent optical phase-shift-keying system”, Optics Express, vol. 17, issue 2, p. 703    [4] W. Shieh and C. Athaudage, “Coherent optical orthogonal frequency division multiplexing,” Electron. Lett., vol. 42, no. 10, pp. 587-589, May 2006.    [5] A. Leven, N. Kaneda, U. V. Koc, Y. K. Chen, Photon. Technol. Lett., 19, 366 (2007).    [6] K. Piyawanno, M. Kuschnerov, B. Spinnler and B. Lank, Paper 7.3.1 in Proc. ECOC '09 (2009)    [7] R. Noe, Photon. Technol. Lett., 17, 887 (2005).    [8] M. G. Taylor, paper Tu4.2.6 in Proc. ECOC '05 (2005).    [9] G. Goldfarb and G. Li, Opt. Express, 14, 8043 (2006).    [10] E. Ip and J. M. Kahn, J. Lightwave Technol, 25, 2675 (2007).    [11] M. Nazarathy et al, J. Lightwave Technol., 26, 1921 (2008).    [12] X. Liu, S. Chandrasekhar, and A. Leven, Opt. Express 16, 792 (2007).    [13] S. Zhang, P. Y. Kam, J. Chen, and C. Yu, Opt. Express 17, 723 (2009).    [14] Nobuhiko Kikuchi, Kohei Mandai, Shinya Sasaki and Kenro Sekine “Proposal and First Experimental Demonstration of Digital Incoherent Optical Field Detector for Chromatic Dispersion Compensation, PDP Th. 4.4.4., ECOC 2006.    [15] Nobuhiko Kikuchi, et al., OFC/NFOEC 2007, PDP21.    [16] Nobuhiko Kikuchi and Shinya Sasaki, “Incoherent 40-Gbit/s 16QAM and 30-Gbit/s staggered 8APSK (amplitude- and phase-shift keying) signalling with digital phase pre-integration technique,”, WD3.2, LEOS '08, 2008.    [17] Nobuhiko Kikuchi and Shinya Sasaki “Optical dispersion-compensation free incoherent multilevel signal transmission over single-mode fiber with digital pre-distortion and phase pre-integration techniques,” paperTu.1.E.2, ECOC 2008.    [18] Nobuhiko Kikuchi and S. Sasaki, “Highly sensitive optical multilevel transmission of arbitrary quadrature-amplitude modulation (QAM) signals with direct detection,” J. Lightwave Technol., vol. 28, pp. 123-130 (2010).    [19] Xiang. Liu, et al., OFC/NFOEC 2007, OtuA6.    [20] Y. Atzmon, M. Nazarathy, “Laser Phase Noise in Differential Optical Transmission Revisited in the Polar Domain,” J. Lightwave Technol., 27, 1, pp. 19-29 (2009).    [21] William Shieh and Keang-Po IIo “Equalization-enhanced phase noise for coherent detection systems using electronic digital signal processing,” OPTICS EXPRESS, Vol. 16, 15718-15727, 2008.    [22] X. Liu, S. Chandrasekhar, and A. Leven, “Digital self-coherent detection,” Opt. Express, vol. 16, pp. 792-803 (2008).    [23] X. Liu, “Receiver sensitivity improvement in optical DQPSK and DQPSK/ASK through data-aided multi-symbol phase estimation,” in Proceedings of European Conference on Optical Communications 2006, Paper We2.5.6, 2006.    [24] X. Liu, “Generalized data-aided multi-symbol phase estimation for improving receiver sensitivity in direct-detection optical m-ary DPSK,” Opt. Express 15, 2927-2939 (2007).    [25] X. Liu, S. Chandrasekhar, A. H. Gnauck, C. R. Doerr, I. Kang, D. Kilper, L. L. Buhl, and J. Centanni, “DSP-enabled compensation of demodulator phase error and sensitivity improvement in direct-detection 40-Gb/s DQPSK,” in Proceedings of European Conference on Optical Communications 2006, post-deadline paper Th4.4.5, 2006.    [26] X. Liu, “Digital self-coherent detection and mitigation of transmission impairments”, 2008 OSA Summer Topic Meeting on Coherent Optical Technologies and Applications (COTA '08), paper CWB2.    [27] N. Kikuchi, K. Mandai, and S. Sasaki, “Compensation of non-linear phase-shift in incoherent multilevel receiver with digital signal processing,” in Proceedings of European Conference on Optical Communications 2007, Paper 9.4.1, 2007.    [28] Y. Takushima, H. Y. Choi, and Y. C. Chung, “Adjustment-free DxPSK receiver based on single delay interferometer using 120-degree optical hybrid,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference on CD-ROM (OFC/NFOEC 2009) (Optical Society of America, Washington, D.C., 2009), paper OMM2.    [29] Y. Takushima, H. Y. Choi, and Y. C. Chung, “Plug-and-play phasor monitor for DxPSK signals based on single delay-interferometer using a 3×3 optical coupler,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference on CD-ROM (OFC/NFOEC 2008) (Optical Society of America, Washington, D.C., 2008), paper OThW4.    [30] Y. Takushima, II. Y. Choi, and Y. C. Chung, “Measurement of differential phasor diagram of multilevel DPSK signals by using an adjustment-free delay interferometer composed of a 3×3 optical coupler,” J. Lightwave Technol. 27(6), 718-730 (2009).    [31] Y. Takushima, H. Y. Choi, and Y. C. Chung, “Enhanced sensitivity of DxPSK receiver by using data-aided phase noise estimation algorithm,” in Opto-Electronics and Communications Conference (OECC 2009), paper WV3.    [32] H. Leib, “Data-aided noncoherent demodulation of DPSK,” IEEE Trans. Commun. 43(2), 722-725 (1995).    [33] Y. Takushima, H. Y. Choi, and Y. C. Chung, “Quality monitoring of DxPSK signals by using differential phasor diagram,” to appear in IEEE Photon. Technol. Lett.